Safety device for presses



Dec. 25, 195] MoLANE SAFETY DEVICE FOR PRESSES Filed May 28, 194'? INVENTOR F/efcher E. M Lane BY M ATTORNEY Patented Dec. 25, 1951 SAFETY DEVICE FOR PRESSES Fletcher E. McLane, Wilkinsburg, Pa., assignor to Westinghouse Electr Pittsburgh, Pa., a corner ic Corporation, East ation of Pennsylvania Application May 28, 1947, Serial No. 750,989

Claims.

This invention relates to fluid-pressure power operated presses and, more particularly, to an improved arrangement of safety control apparatus for operating such presses or similar machines.

Many machines such as power presses have a working member which is moved at a high velocity to perform a working operation. Where the article on which the working'member performs its operation is positioned manually by v involved in ally operable control members such as push buttons which are mounted in spaced relation so as to require the use of both hands in order to operate the work performing machine. Where machines have been provided with control apparatus requiring the use of both hands to operate the same, it has been found that some operators will defeat the purpose of such control apparatus by taping down or otherwise securing one of the control members so that the machine may be operated by one hand.

One of the principal objects of this invention is to provide an arrangement of control apparatus requiring the use of both. hands for operating a power press or similar machine which will effectively prevent the operator from tampering with the control apparatus so as to render it operable by one hand. To this end, there is provided an electrical control circuit having a pair of manually operable push-button switches for controlling the operation of a machine together with a novel arrangement of control mechanism for rendering the push-button switches inoperative to operate the machine in the event that only one of the switches is operated. Each of the switches is operatively associated with a transformer having a primary winding which is energized upon operation of the switch. The secondary windings of the transformers are connected in a series circuit in such manner that no current flows therein, when both of the push-button switches are operated concurrently in their normal fashion, in which case the primary windings of each transformer will be energized at the same time. However, in the event that only one of the pushbuttoncontrol switches is operated, a current will flow in the series circuit connecting the secondary windings of the transformers, and this current is utilized to interrupt the control circuit to the machine so as to effectively prevent its operation.

Other objects and advantages of the invention will become apparent from the following description.

In the drawing there is shown a preferred embodiment of the invention. In this showmg:

Figure 1 is a diagrammatic illustration of a fluid pressure operated press of the type with which this invention is concerned, and

Figure 2 shows the control circuit which is used in connection with the manually operable control members for the press shown in Figure 1.

Referring to Figure l, the press there shown comprises a cylinder 6 carried by supporting members 2 mounted on a work bench 3 to which is secured a stationary platen 4. A piston 5 is mounted in the cylinder 1 and is provided with av piston rod 6 having one end projecting from the cylinder and carrying a movable platen I. Fluid-pressure, such as compressed air or some other suitable fluid medium under pressure, is admitted to the cylinder I through conduits 8 and 9 from a supply conduit it under the control of a valve H. The valve H is provided with a spring 12 biasing it to a position connecting the conduit 8 and upper end of the cylinder I to the atmosphere through an opening l3 and connecting the conduit 9 and lower end of the cylinder l to the fluid pressure supply conduit iii. The valve H is provided with a movable armature M. and an operating coil [5 for moving the armature to thus operate the valve against the bias provided by the spring i 2 to a position connecting the conduit 9 and lower end of the cylinder i to the atmosphere through an opening it and connecting the upper end of the cylinder i and conduit 8 to the fluid pressure supply conduit IE. Upon energization of the operating coil I5, fluid pressure will be admitted to the upper end of the cylinder I and the piston 5 will be moved downwardly at a high velocity carrying with it the movable platen l which will operate to perform useful work on a work-piece disposed on the stationary platen 4.

Manually operable push-button switches I? and [8 are provided for controlling the energization of the operating coil 55. The push-button switches I? and I3 are mounted on arms is secured to the supporting members 2. The mounting of the push-button switches ii and It in spaced relation requires the use of both hands in order to operate the press and will prevent operation of the press at any time when the operators hands are in the path of travel of the movable platen 1.

Referring to Figure 2, there is shown the circuit by which the operating coil for the armature i4 is connected across alternating current supply leads and 2!. This circuit is completed by a movable contact member 22 carried by the push-button switch l1, and a movable contact member 23 carried by the push button l8 upon operation of the push buttons l1 and 19 to move the movable contact members 22 and 23 to positions bridging the stationary contacts 24 and 25, respectively. This circuit also includes a safety contactor indicated as a whole by the numeral 26 and comprising a stationary contact 21 and movable contact 28. The push buttons 11 and it are provided with springs 29 biasing them to an inoperative position with the contact members 22 and 23 engaged with stationary contacts 30 and 3|, respectively, for a purpose to be described.

The parts of the circuit in Figure 2 included within the broken line 32 comprise the safety control apparatus which operates the contactor 26 to disengage contact 28 from contact 21 to prevent energization of the operating coil is when only one of the switches is operated. These parts are normally mounted in a control box 33 carried by the press as shown in Figure 1. This apparatus includes a transformer 34 associated with the push button l1 and a transformer 35 associated with the push button IS. The transformer 34 is provided with primary and secondary windings 36 and 31, and the transformer 35 is provided with primary and secondary windings 38 and 39. Energization of the primary winding 36 by the alternating current leads 29 and 2| is under the control of contacts push button I! which operates to bridge the stationary contacts 4! upon movement of the push button l1 against the bias of its spring 29. Similarly, energization of the primary winding 38 of the transformer 35 is effected by contacts 42 carried by the push button l8 which operates to bridge stationary contacts 43 upon movement of the push button it against the bias of its spring 29. The secondary windings 31 and 39 have their terminals connected in a series circuit which includes the heating resistor 44. The polarity of the connections of the secondary windings 31 and 39 is selected in such manner that no current will flow through the heating resistor 44 when both of the secondary windings 31 and 39 are energized by their respective primary windings. Adjustable resistances 45 and 46 are included in the circuits of the primary windings 36 and 38 respectively, for a purpose to be described.

A bimetallic thermal element 41 is mounted ad-- jacent the resistor 44 so as to be subjected to the heat developed thereby when current flows through the resistor 44 upon energization of only one of the primary windings 31 and 39. The thermal element 41 has one end secured to a stationary support 48, and its free end 49 in engagement with a member 59 which carries the movable contact 28 and constitutes part of the safety contact structure 26. The member 53 is mounted for pivotal movement about a pivot 5i and is provided with a spring 52 biasing it for movement in a counterclockwise direction to disengage contact 28 from contact 21. Counterclockwise movement of the member by its bias is normally prevented by engagement of the member 50 with the end 49 of the bimetallic thermal ele- 40 carried by the v ment 41. When the thermal element 41 is subjected to heat by its heater 44, the free end 49 thereof will move upwardly to a position opposite an opening 53 formed in the member 50. When the end 49 is aligned with the opening 53, the bias on the member 50 provided by the spring 52 will be effective to move the member 50 in a counterclockwise direction to disengage the movable contact 28 from the stationary contact 21 and thereby prevent energization of the operating coil l5. When the contacts 21 and 28 are disengaged by operation of only one of the switches l1 and [8 in a manner to be explained, it is necessary to manually reset the contact structure 26 in order to efiect subsequent operation of the press. An adjusting element 54 is provided for regulating the position of the free end 49 of the bimetallic thermal element 41 with respect to the opening 53 to thereby vary the time which it will take for the thermal element to operate.

When both of the push buttons l1 and I8 are operated in their intended manner, the contacts 22 and 23 function to complete the circuit to the operating coil l5 for the armature l4 which in turn effects operation of the press through actuation of the valve ll. At the same time, the contactors 49 and 42 will energize the primary windings 39 and 38 of the transformers 34 and 35, respectively, and under this condition no current will flow through the secondary windings 31 and 39 since such windings are connected in phase opposition in a series circuit. Consequently, no current will flow through the heating resistor 44, and the thermal element 41 will not operate the safety contact structure 26.

However, in the event that only one of the switches H or I8 is operated, then only one of the primary windings of the transformers 34 and 35 will be energized. Assuming that the switch 11 is operated, then the primary winding 36 will be energized and current will be induced in the secondary winding 31. Since at this time the primary winding 38 will be deenergized, there will be no current induced in the secondary winding 39 to oppose the current induced in the secondary winding 31, and the current induced in the secondary winding 31 will flow through the resistance 44 which will operate to heat the bimetallic thermal element 41. Under this condition, the bimetal 41 will operate in a short period of time to open the contacts 21 and 28.

When the switch I8 is not operated at all, the contacts 23 will bridge the stationary contacts 3! and provide a short circuit shunt across the deenergized secondary winding 39, through the leads 55 and 51. A lead 56 is provided in connection with the stationary contacts 36 on the push button [1 for a purpose similar to that of the lead 55. When the deenergized secondary winding is provided with a short circuiting bridge by the contacts 22 or 23 through non-operation of one of the switches l1 and I8, the thermal element 41 will operate in a very short period of time. When one of the switches 11 or I8 is only partially operated, then the contacts 39 or 3| will not be connected and the impedance of the deenergized secondary winding 39 will be directly in series with the resistance 44. Under this condition, the current flowing through the resistor 44 will be reduced and it will take the thermal element 41 a longer period of time to operate. The length of this period of time may be adjusted by varying the resistance 45 or 46 in the circuits of the primary windings 39 and 38.

From the foregoing, it will be seen that there is provided an effective manually operable controlfora power press or similar machine which requires theme of two hands to operate the machine. The arrangement of the transformers 34 and 35 effectively prevents an operator from interfering with the safety features of the apparatus as by tying or taping down one of the manually operable members I! or 18. The operator is thus prevented from tampering with the controls and thus injuring himself in the operation of the machine.

Since certain changes may be made in the above described construction and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all the matter contained in the above description and shown in the accoi panying drawing shall be considered as illustrative and not in a limiting sense.

I claim as my invention:

1. In a safety control, a pair of manually operable control members normally effective upon concurrent operation thereof to perform 'a control operation, a thermal element operable upon heating thereof to prevent a control action by said members, and means operative to heat said thermal element when only one of said control members is operated, said means being inoperative to effect a heating action when both of said control members are operated.

2. In a safety system, in combination, a pair of supply terminals, a control circuit, a pair of manually operable control members normally effective upon concurrent operation thereof to connect said control circuit to said terminals to perform a control operation, a thermal element operable upon heating thereof to prevent a control action by said members, and heating means for said thermal element comprising a pair of transformers respectively having primary and secondary windings, each of said primary windings having a switch operable by one of said control members for controlling the energization thereof, and a circuit connecting said secondary windings in series opposition in which current flows when only one of said primary windings is energized by operation of one of said switches, the heating of said thermal element being effected by current flowing in said circuit.

3. In a safety system, in combination, a pair of supply terminals, a control circuit, a pair of manually operable switches operable concurrently to connect the control circuit to said terminals and mounted in such spaced relation to each so as to require the use of two hands to effect concurrent operation thereof, a pair of transformers having primary and secondary windings, each of said switches having contacts controlling the energization of one of said primary windings whereby concurrent operation of said switches effects similar energization of said primary windings, said secondary windings being connected in a series opposition circuit so that no current flows therein when both of said switches are operated and in which current flows when only one of said switches is operated, auxiliary contact means in said control circuit, and means responsive to current flowing in said series circuit for operating said auxiliary contact means.

4. In a safety system, in combination, a pair of supply terminals, a control circuit, a pair of manually operable switches operable concurrently to connect said control circuit to said supply terminals to complete said circuit and mounted in such spaced relation to each other so as to require the use of two hands to effect concurrent operation thereof, a pair of transformers having primary and secondary wind-- ings, each of said switches having contacts controlling the energization of one of said primary windings from said supply terminals whereby concurrent operation of said switches effects similar energization of said primary windings, said secondary windings being connected in a series opposition circuit so that no current flows therein when both of said switches are operated and-in which current flows when only one of said switches is operated, auxiliary contact means in said control circuit, and a thermal element controlling operation of said auxiliary contact means, said thermal element being effective to operate said contact means upon being subjected to heat, the heating of said thermal ele-' ment being responsive to current flowing in said secondary circuit.

5. In a safety system, in combination, a pair of supply terminals, a control circuit, a pair of manually operable switches operable concur rently to connect said control circuit to said ter minals to complete said circuit and mounted-iii such spaced relation to each other so as to re-" quire the use of --two hands to effect concurrent operation thereof, a pair of transformers having primary and secondary windings, each of said switches having contacts controlling the energization of one of said primary windings from said sup-ply terminals whereby concurrent operation of said switches effects similar energization of said primary windings, said secondary windings being connected in a series opposition circuit so that no current flows therein when both of said switches are operated and in which current flows when only one of said switches is operated, auxiliary contact means in said control circuit, a thermal element controllin operation of said auxiliary contact means, and a resistance heater in said series opposition circuit for heating said thermal element so that said auxiliary contact means will be operated to open said control circuit when current flows in said series circuit.

6. A circuit as claimed in claim 3 wherein each of said transformers is provided with a resistance in the circuit of its primary winding for reducing the impedance of its secondary windmg.

7. A circuit as claimed in claim 3 wherein the secondary winding of the transformer associated with the switch which is not operated is provided with a short circuit shunt in said series circuit to increase the current flow in said series circuit when only one of said switches is operated.

8. In a safety control, in combination, a pair of electric supply terminals, a control circuit including means for effecting a control operation upon energization of said circuit and including a normally closed switch, a pair of manually operable switches effective upon concurrent operation to connect said control circuit to said supply terminals, a pair of transformer primaries also connected to said supply terminals upon concurrent operation of said switches, transformer secondaries connected in series opposition, whereby no current will fiow in the secondary circuit upon concurrent operation of said switches, circuit means for connecting only one transformer primary to said supply terminals upon non-concurrent operation of said switches, whereby a current is caused to flow in thetransformer secondary circuit, and means responsive to the current flow in the transformer secondary circuit for effecting the opening of said normally closed switch.

9. In a safety control, in combination, a pair of electric supply terminals, a control circuit eifecting a control action when connected to said terminals, normally closed switching means included in said control circuit, a pair of manually operable spaced switching means effective upon concurrent operation thereof to effect connection of said control circuit to said terminals, and means responsive to non-concurrent operation of said manually operable switching means for effecting the opening of the normally closed switching means.

10. In a safety control, in combination, a pair of electric supply terminals, a control circuit including means operable, upon connection of said circuit to said terminals, to produce a control action, thermally responsive control means included in said control circuit for opening said control circuit, a pair of manually operable switching means efiective upon concurrent operation to connect said control circuit to said supply terminals, said switching means being spaced from each other a sufficient distance that an attendant operating said switching means must use both hands, and heating means responsive to non-concurrent operation of said switching means for causing the operation of said thermally responsive control means.

11. In an electric safety control, in combination, a pair of alternating current supply terminals, control circuit means, a pair of manually operable control switches effective upon concurrent operation thereof to connect said control circuit means to said supply terminals to institute a control action, said switches being so spaced from each other that the attendant operating the switches must use both of his hands,

a pair of electric transformers connected to be I energized by the operation of said switches, said transformers having primary and secondary windings with the secondary windings connected in a series opposition circuit so that no current flows in the series opposition circuit when both of said transformers are simultaneously energized, and a thermal element operable upon being subjected to heat to prevent said control action by said control circuit, the heating of said thermal element being responsive to current flowing in said series opposition circuit.

12. In a two handed safety controller for a power operated machine, the combination of an actuator for said machine arranged to be connected to a source of power, a pair of mechanisms operable concurrently for connecting the actuator to the source of power, and means operable a preselected time after operation of one of said mechanisms for disconnecting said mechanisms from the source of power whereby to prevent operation of the actuator upon operation of the other of said mechanisms after the lapse of said predetermined time.

13. In a two handed safety controller for a power operated machine, the combination of an actuator for said machine arranged to be connected to a source of power, a pair of mechanisms for connecting the power to the actuator and requiring concurrent operation, and means operable when only one of said mechanisms is operated for preventing the connection of said actuator to said source of power.

14. In a safety controller, the combination of an actuator for a machine arranged to be connected to a source of power, a pair of manually operated mechanisms for connecting the power to the actuator and requiring concurrent operation, a disconnecting device operable to prevent flow of power to said actuator, and means operable to actuate said disconnecting device in the event of operation of one of said mechanisms upon the lapse of more than a preselected time after operation of the first of said mechanisms.

15. In a safety controller, the combination of an actuator arranged to be connected to a source of power, a pair of mechanisms for connecting the actuator to the source of power and requiring concurrent operation, timing means operable for disconnecting said actuator from said power source unless both mechanisms are operated within a preselected time interval, and means for adjusting said timing means whereby the period of time may be varied.

FLETCHER a. MCLANE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,052,795 Rapisarda Sept. 1, 1936 2,404,980 Munschauer, Jr. July 30, 1946 

